This paper proposes a dual-polarized omnidirectional antenna for base-station antennas that are mounted on the rooftops of buildings. The antenna suppresses the degradation in the received-signal level due to the inclination of mobile antennas in the personal handy-phone system (PHS). The proposed polarization-diversity antenna is comprised of a dielectric-loaded slotted-cylinder antenna for horizontally polarized waves and a conventional collinear array antenna for vertically polarized waves in a height-diversity configuration. The structure of the proposed antenna and its fundamental characteristics, such as the input impedance and radiation pattern, are shown. The change in the radio zone length (RZL) due to the inclination angle of the mobile antenna is measured to estimate the improvement offered by the proposed antenna in an urban area. It is shown that the RZLs of the collinear antennas in line-of-sight (LOS) environments are decreased by 73% when the mobile antenna is inclined at 90 , whereas the proposed polarization-diversity antenna restrains the degradation to approximately 20%, regardless of the inclination angle without downtilt and from 20% to 40% for a 15 downtilt. The RZLs of the collinear tilt antennas in non-LOS (NLOS) environments are below approximately 20%, compared to those of the collinear tilt antennas for the LOS route. We show that the RZLs in the NLOS environments are short compared to those for the LOS environments in microcell systems such as PHS with a high-elevation base station, even when the polarization-diversity technique is applied to the base station.